1. Field of the Invention
The present invention relates to a thermal head, a printer, and a method of manufacturing a thermal head.
2. Description of the Related Art
Conventionally, as a thermal head used in a thermal printer, one in which a plurality of heat generating resistors and electrode portions are formed on a laminated substrate of a support substrate and an upper substrate which are formed of the same glass material is known. The thermal head is configured to print on a heat-sensitive recording medium or the like by causing the heat generating resistor to generate heat through supply of electric power to the electrode portion.
Further, the thermal head has a cavity portion in a bonded portion of the support substrate and the upper substrate in a region which is opposed to the heat generating resistor. The cavity portion functions as a heat insulating layer, thereby reducing the amount of heat transferred from the heat generating resistor via the upper substrate to the support substrate side. Further, by forming the support substrate of a glass material having a low thermal conductivity, heat transferred via the cavity portion to the support substrate side is stored in the support substrate to raise the temperature of the entire surface of the thermal head. In other words, due to high heat insulating performance of the cavity portion immediately below the heat generating resistor and a thermal storage effect of the support substrate made of a glass material, the thermal head uses heat generated by the heat generating resistor more efficiently to realize high heat generating efficiency.
An application period for a thermal head, during which one print dot is formed on a heat-sensitive recording medium, includes heating time for heating the heat generating resistor for printing, and non-heating time for cooling the heated heat generating resistor. While the rise time of the temperature during the heating time is proportional to a thermal capacity C around a heat generating portion of the thermal head, the fall time of the temperature during the non-heating time depends on the thermal capacity C and a thermal conductivity G of the thermal head and is proportional to C/G.
In this thermal head, while the cavity portion reduces the thermal capacity to obtain a fast response characteristic of the heat generating resistor during the heating time, the temperature of the heat generating resistor which has once increased is less liable to fall due to the thermal storage effect of the support substrate, and thus, the response characteristic of the heat generating resistor during the non-heating time is slow to prolong the non-heating time.
Accordingly, in this field, a thermal head and a printer which can attain both higher printing speed and reduced power consumption, and a manufacturing method which can manufacture such a thermal head with ease are desired.